As a conventional electronic cam type rotary cutter control method, for example, “an electronic cam type rotary cutter control method and an electronic cam curve generating method” has been disclosed in JP-A-2000-198094 publication (Patent Document 1). As shown in FIG. 6, an electronic cam curve including a prediction over a next cycle is generated to control, by utilizing a servomotor, an apparatus for defining the motion of a specific portion in one cycle constituting a non-cutting section and a cutting section in a rotary cutter for continuously cutting a web-like paper or an iron plate flowing consecutively into a set length without carrying out a rest. In this case, an electronic cam curve is represented by a speed pattern in FIG. 8(a) and a position pattern in FIG. 8(b), and a section (2)=T1→T2=T12 indicates the non-cutting section and a section (3)=T2→T3=T23 indicates the cutting section, and a position curve in FIG. 8(b) is represented by a cubic, and the position curve is differentiated so that a speed curve is represented by a quadric shown in FIG. 8(a).
Moreover, a cam curve in this case can automatically correspond, in an identical algorithm, to the case in which a cutting length is greater than the circumference of a cutter and the case in which it is smaller than the circumference.
In an electronic cam control to be carried out by using the cam curves for a speed and a position, as shown in FIG. 6, a pulse is fetched from a measure ring and roll 2 for detecting the amount of travel of a processed product such as a paper or an iron plate and an integration is carried out by means of a counter A15. Consequently, a phase θ in one cycle which has a maximum value of a pulse amount θM corresponding to a cutting length is repetitively obtained by a triangular wave generating circuit 17. The phase θ is input to a position pattern generating circuit 21 and a speed pattern generating circuit 19 corresponding to one cycle based on the cam curve so that a position command and a speed command are obtained every minute. Referring to the position command, when one cycle is ended, the maximum value of the position of the cycle (the amount of the rotating pulse of a servomotor 3 corresponding to a cutting length) is added so that a rotary cutter is controlled to be continuously rotated in the same direction.
For the position command thus generated, a feedback control is carried out based on a pulse count value sent from PG4 of the servomotor 3 and a position control is executed in order to cause a position deviation to approximate to zero, and an electronic cam control is thus performed every minute. On the other hand, referring to a speed pattern, an output from the speed pattern generating circuit 19 is multiplied by a speed obtained by a differentiating circuit 16 so as to be used for a feedforward corresponding to the running speed of an actual processed product, thereby enhancing a follow-up property.
In the conventional art, however, when the cutting length is caused to be extremely greater than the circumference of a cutter, the degree of a decrease in a quadratic curve in a non-cutting section in a speed pattern is increased so that a section in which the speed pattern is minus as in a reverse rotating section is generated as shown in a speed pattern in case of a great length in FIG. 7(a). In some cases, consequently, the cutter roll carries out at least one reverse rotation. Therefore, there is a problem in that a mechanical trouble is made, that is, “an object to be cut crashes against a blade rotated reversely”.
Therefore, it is an object of the invention to provide a reverse rotation preventing electronic cam curve generating method of an electronic cam type rotary cutter control and a control apparatus thereof in which such a speed pattern as not to be minus is previously formed and the stoppage of a cutter and the interruption of an operation can be prevented also in case of a very great cutting length, the reverse rotation of the cutter can be prevented, and a mechanical trouble that an object to be cut crashes against a blade rotated reversely can be avoided.